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<p>This study examines how travel speed (18, 22, 36&#xa0;mm·min<sup>−1</sup>) and plunge depth (1.55, 1.60, 1.65&#xa0;mm) affect material flow, microstructure, and mechanical properties of friction-stir-welded (FSW) JIS G3131 SPHC steel at a constant 250&#xa0;rpm. Weld quality was governed by thermo-mechanically driven plastic flow: suitable parameter combinations ensured uniform heat input and sufficient plasticization, promoting dynamic recrystallization and fine equiaxed grains in the nugget zone (NZ). The finest average grain size, 3.19&#xa0;μm, occurred at 22&#xa0;mm·min<sup>−1</sup>/1.55&#xa0;mm and corresponded to a peak NZ-top hardness of 316.5 HV beneath the tool shoulder. The optimal joint (18&#xa0;mm·min<sup>−1</sup>/1.60&#xa0;mm) achieved a balanced thermo-mechanical state, delivering an ultimate tensile strength of 490&#xa0;MPa (121% of base metal) and a yield strength of 456&#xa0;MPa (136%); all fractures occurred in the base metal, indicating a sound metallurgical bond. Conversely, excessive travel speed or inappropriate plunge depth produced surface underfill or root voids and reduced strength. These results establish a quantitative process–structure–property relationship that guides parameter selection for robust, high-strength FSW joints in low-carbon steels.</p>

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Impact of Process Parameters on the Strength and Integrity of FSW Low-Carbon Steel Joints

  • 期刊论文

  • 发表日期：

    2026年2月5日

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  • Cheng-Yu Lu,
  • Jung-Shiuan Lu,
  • Yun-Hao Han,
  • Ren-Yu Chen

摘要

This study examines how travel speed (18, 22, 36 mm·min−1) and plunge depth (1.55, 1.60, 1.65 mm) affect material flow, microstructure, and mechanical properties of friction-stir-welded (FSW) JIS G3131 SPHC steel at a constant 250 rpm. Weld quality was governed by thermo-mechanically driven plastic flow: suitable parameter combinations ensured uniform heat input and sufficient plasticization, promoting dynamic recrystallization and fine equiaxed grains in the nugget zone (NZ). The finest average grain size, 3.19 μm, occurred at 22 mm·min−1/1.55 mm and corresponded to a peak NZ-top hardness of 316.5 HV beneath the tool shoulder. The optimal joint (18 mm·min−1/1.60 mm) achieved a balanced thermo-mechanical state, delivering an ultimate tensile strength of 490 MPa (121% of base metal) and a yield strength of 456 MPa (136%); all fractures occurred in the base metal, indicating a sound metallurgical bond. Conversely, excessive travel speed or inappropriate plunge depth produced surface underfill or root voids and reduced strength. These results establish a quantitative process–structure–property relationship that guides parameter selection for robust, high-strength FSW joints in low-carbon steels.